Sub-cyclic measurements of speed and time for internal combustion engine horsepower indication

ABSTRACT

Indications of speed of an internal combustion engine are derived from an engine member rotating directly with the crankshaft, such as the teeth on the flywheel, so as to provide indications for speed measurements on a sub-cycle basis (that is, many times during each revolution), a timer is started after a threshold speed is reached as determined by comparison with the sub-cyclic speed indications, and a measurement of speed is made contemporaneously with starting the counter; after an elapsed time interval which may be on the order of several cycles, which is determined by the acceleration of the engine, the timer is stopped and the speed is once again measured. In one embodiment, the speed is continuously compared against an upper reference speed during the interval that the timer is running, and when the upper reference speed is reached, the timer is stopped. In a second embodiment, the interval of the timer is fixed, and instantaneous speed is measured at time-out. In either instance, the starting speed, the stopping speed, and the elapsed time are all accurately related and may be utilized in accordance with known techniques for computing factors relating to torque and horsepower.

CROSS REFERENCE TO RELATED APPLICATIONS

Some of the subject matter disclosed herein is disclosed and claimed ina commonly owned copending application filed on even date herewith byWillenbecher et al, Ser. No. 684,219, entitled SUB-CYCLIC SPEED ANDCYCLIC TIME MEASUREMENTS FOR INTERNAL COMBUSTION ENGINE HORSEPOWERINDICATION.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to diagnosing internal combustion engineselectronically.

2. Description of the Prior Art

In the measurement of factors relating to the general health of theengine, it has been known to provide indications related to torque,which then may be related through speed to horsepower, to provide ageneral indication of engine health. It is well known that horsepower isthe product of speed and torque; torque, on the other hand is a functionof acceleration and inertia; thus horsepower can be taken as someconstant times speed and acceleration. If the acceleration and the speedare taken at the same speed, then error exists only in the fact that theresulting measured horsepower includes factors related to frictionaldrag and loading of the engine (such as by engine accessories). However,it is known that these factors can be accommodated by emperical formulasof various kinds.

In one technique known to the art, the engine is allowed to undergo aburst acceleration from a low speed to a high speed, the speed of theengine is monitored, and the elapsed time between sensing of first andsecond speeds is measured. The problem in this technique is that thespeed measurement is made over an entire engine cycle, so the precisetime at which the engine crosses the lower threshold speed and the upperthreshold speed, thereby to accurately measure the time intervalrequired for the engine to accelerate from one speed to another, cannotbe known. In this technique, interpolation based on the differencebetween the average speeds sensed over succeeding cycles and the desiredthreshold speeds is utilized to correct the time increment otherwisemeasured between cycles which follow the sensing of threshold speeds. Itis alleged that such a technique eliminates errors resulting fromsub-cyclic speed variations which are known to occur in internalcombustion engines as a result of the individual cylinder contributionsto acceleration when combustion occurs and the individual contributionsto cylinders to deceleration during compression for that cylinder;however, the errors resulting from gross interpolation to estimatespeeds within each cycle of the engine may well exceed the cyclicvariations overcome thereby.

SUMMARY OF THE INVENTION

Objects of the present invention include provision of sub-cyclic speedmeasurements in internal combustion engines and accurate correlation ofspeed and time in measurements made relating to engine acceleration foruse in horsepower indications.

According to the present invention, measurement of acceleration of aninternal combustion engine while utilizing its own inertia, drag andaccessory loading as an engine load, is accurately made by utilizingsubstantially instantaneous, sub-cyclic speed measurements at theprecise times of starting and stopping an interval timer whichaccurately measures elapsed time over a significant fraction of theacceleration of the engine which is at least greater than one enginecycle. According further to the invention, speed of the engine ismonitored as the engine accelerates, and once a beginning thresholdspeed is reached, an interval timer is engaged commensurately with anaccurate recordation of speed, and following an interval which is eitherspeed-dependent or fixed, the interval timer is disengagedcommensurately with an accurate recordation of speed; the actual,substantially instantaneously measured speed, determined on a sub-cyclebasis, thereby correlates exactly with the extent of the timed interval.

In accordance with one aspect of the invention, measurement ofpredetermined beginning and ending speed, regardless of the portion ofan engine cycle in which they actually occur, is used to start and stopan interval timer. In accordance with another aspect of the invention,the time interval is fixed; achieving a first speed starts the interval,and time-out causes measurement of the second speed.

The present invention, by utilizing substantially instantaneous speedreadings allows accurate measurement of speeds to define a time intervalwhich spans a significant portion of the acceleration pattern of anengine, thereby providing a simple method of indicating averageacceleration for use in torque and horsepower calculations. Starting andstopping of the time interval in response to sensing on an instantaneousbasis the achievement of predetermined speeds provides for a constantchange in speed, thereby avoiding the necessity for calculations todetermine the change in speed over the time interval.

The foregoing and other objects, features and advantages of the presentinvention will become more apparent in the light of the followingdetailed description of preferred embodiments thereof, as illustrated inthe accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a simplified schematic block diagram of a diagnostic systemincluding engine parameter sensing apparatus and exemplary electronicprocessing apparatus, in which the present invention may beincorporated;

FIG. 2 is a simplified block diagram of engine parameter sensingapparatus for use in the embodiment of FIG. 1; and

FIG. 3 is a simplified schematic diagram of tooth timer means forobtaining instantaneous, sub-cyclic engine speed in the embodiment ofFIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to FIG. 1, a system which may incorporate the presentinvention is illustrated as representing the architecture of a typicaldata processing system or computer together with special purposeapparatus related to an engine diagnostic system of the type in whichthe invention may be incorporated. Specifically, the system incorporatesengine sensors and signal conditioners 10 of a well known type which areadapted to be disposed for response to various parameters or discreteconditions on an engine under test, as described more fully hereinafter.Some of the sensors relate to pressures, temperatures and the like andare therefore analog signals, the magnitude of which is a measure of theparameter being sensed. The outputs of the sensors are fed over lines 13to an analog to digital converter (A/D) 11 when selected by an A/Dmultiplexer 12 in response to a particular sensor address appliedthereto by the program of the data processor. In addition, a toothsensor may sense the passage of teeth on the flywheel of the engine toprovide a tooth signal on a line 14, the intertooth time interval ofwhich (when the engine is running) is measured by a tooth timer 15 andprovided on tooth count lines 16. Another discrete signal is a cylinderor cycle identification signal (CID) on a line 17 which is applied to aCID centering circuit 18 to provide a CID signal on a line 19. The rawCID signal on the line 17 is a signal from a proximity sensor disposedto sense movement of an engine member once in each cycle of the engine,such as the rocker arm for the intake valve of one of the cylinders or acam, if desired; this provides information of the cylinder-by-cylinderposition of the engine at any moment in time in the same fashion as thenumber one firing in a spark ignition engine, and also providescycle-to-cycle division of the engine's angular position as it isrunning or cranking.

In accordance with the invention, the parameters of the engine asprovided through the A/D converter 11, and the instantaneous positioninformation with respect to the engine as provided by the CID signal onthe line 17, and the tooth signals on the line 14 may be used indiagnosis of the engine in accordance with the invention herein.

Additional special apparatus which may be used (although as describedhereinafter is not necessarily required) includes a tooth counter anddecode circuit 20, and a pair of counters 20a, 20b referred to ascounter 1 and counter 2, and an interval timer 20c, and special purposeregisters 22, which may be used (as an alternative to memory) to retaincertain factors that are used so often as to render it advisable to havethem directly available to the program rather than having to access themin memory, in order to cut down processing time and complexity ofprogramming. Such registers may contain factors utilized in processingdata (such as multiplicands used in digital filtering of the data andthe like) and information relating to the particular engine under test(such as number of strokes and cylinders) which may be entered byswitches manipulated by an operator, the switches feeding binary decodecircuits such that the decode constantly reflects the position of theswitch on a steady state basis in the manner of a register.

The remainder of FIG. 1 is illustrative of one type of data processingapparatus, which is shown for illustrative purposes herein since it is atype that may be advantageous for use where general purpose programmingis not required, but rather limited functions are to be performed. Acomputer, as is known in the art, includes memory (or accessiblestorage), and arithmetic unit, program control, and the necessary gates,data flow and event decode or monitoring circuits so as to permitadvancing logically through the steps which are to be performed.Specifically, a memory 24 may be loaded from a variety of inputs shownon the data flow under control of a memory multiplexer 25 which isenabled and addressed by the program so as to select which of thepossible inputs to memory are to be applied thereto, if any. The memory24 is responsive to a memory address register 26 which may respond to acounter used in program control in a usual fashion. The output of thememory is available to other portions of the data flow, such as printand display apparatus 27 and the arithmetic apparatus includingarithmetic unit input registers, referred to herein as an A register 30and a B register 31 under control of register gates 32 which arecontrolled by the program in a known fashion. Herein, the output of theA register and the B register is available to the register gates 32 andto the main data flow, so that their contents may be moved between theregisters 30, 31 or to the memory 24. This is to facilitate theparticular type of processing which may be employed in an enginediagnostic system, as is described more fully hereinafter. The registers30, 31 feed an arithmetic unit of a known type 35, the function ofwhich, controlled by the program, is to add, subtract, multiply ordivide, to provide answers to a result register 36 as well as providingindications of the sign of the result. As indicated in FIG. 1, theresult register may be available at the input to the arithmetic unitthrough the gates 32; alternatively, as is common in many computers theresult register could be automatically one of the inputs to thearithmetic unit, and it can be loaded directly from the memory upon aproper command.

In order to provide data inputs to the memory for initialization and topermit a degree of control over the system during processing, a keyboard38 of a usual variety may be provided. In addition to data inputs, thekeyboard may have control function keys that permit choice to theoperator of loading memory from the result register or of loading memoryin response to the keyboard, depending upon conditions which may bedisplayed in the print and display apparatus 27.

For the rather limited number of test being performed in apparatusincorporating the present invention, the program may be controlled in avariety of ways. One way is a program ROM 40 which provides input gateaddresses to control the inputs to the memory, the arithmetic inputregisters, and the A/D converter, etc.; the memory address; thefunctions to be performed by the arithmetic unit, and other commandssuch as commands to the memory to cause it to read or write, and tostart the A/D converter 11, and the like. Sequencing is controlled byunconditional branch instructions (which provide a branch address) andby skip instructions (dependent on conditions) provided to a branch/skipcontrol 42 at the input to the program counter 44, which is alsoresponsive to system clocks 46. Thus, as is known, for each programclock signal received from the system clocks, the program counter may beadvanced, skipped once or twice, or reset to the branch address, independence upon the presence of branch or skip instructions.

It should be understood that the particular processing apparatus used,and the degree of use of special purpose apparatus, is dependent uponthe particular implementation of the present invention which is to bemade, and forms no part of the present invention. If the invention isutilized in a complex, sophisticated diagnostic system in which avariety of diagnostic functions are required, then the type of apparatusselected for processing may be more sophisticated and capable of generalpurpose utilization in order to accommodate the special requirements ofall of the diagnostic procedures to be performed. However, the cost ofprogramming complexity of such a processing system may be unwarranted ina diagnostic system which performs either relatively few or relativelysimple tests. As is more apparent in the light of detailed operationaldescriptions hereinafter, well known processing systems (such as NOVAand PDP/11) employing only programs provided through techniques wellknown in the art, may be utilized in conjunction with the engine sensorsand conditioners 10, suitable input and output apparatus (such as thekeyboard 38 and the print and display apparatus 27) and, depending onthe processing power of the data processing system selected, somespecial purpose hardware which may be found advisable, such as the toothtimer 15, the tooth counter 20 and some special registers 22. However,the well known processing systems referred to hereinbefore can provideadequate memory capacity to perform the tooth timing and countingfunctions, and to provide for the storage of all required parameters andengine information in the memory, as is readily apparent to thoseskilled in the art.

Referring now to FIG. 2, a plurality of engine sensors in a diagnosticsystem incorporating the present invention may include, among others nowshown in FIG. 2, a starter voltage probe or clamp 46, a starter currentprobe 47, an atmospheric pressure transducer 48, which could be disposedin general proximity to the engine under test, a pressure transducer 49to measure the intake manifold air pressure, a filter pressuretransducer 50 to measure the pressure of the fuel downstream of the fuelinlet filter, a fuel pressure transducer 51 to measure the pressure atthe fuel injector inlet rail of the engine, a coolant pressuretransducer 52 which may preferably measure the pressure of coolant atthe inlet to the coolant thermostat, a coolant temperature transducer 53to measure coolant temperature, preferably at the inlet to thethermostat. In a diagnostic system incorporating the present inventionthere may also be a proximity sensor 54, which may comprise an RGT Model3010-AN Magnetic Proximity Sensor, provided by Electro Corporation,Sarasota, Florida, for sensing the passage of flywheel teeth past aparticular point adjacent to the flywheel housing, and a proximitysensor 55 such as a Model 4947 Proximity Switch distributed by ElectroCorporation, for sensing the presence of an engine member which moves ina unique fashion once in each cycle of the engine, which is onerevolution in a two stroke engine or two revolutions in a four strokeengine. The proximity sensor 55 may preferably be mounted through thevalve cover adjacent to a rocker arm related to the intake valve of oneof the cylinders of the engine, thereby to provide information as to theparticular point of an engine cycle once in each cycle, as well as todelineate successive engine cycles as the engine is rotating.

Each of the sensors of FIG. 2 is applied to a suitable one of aplurality of signal conditioners 56, 57 to filter out unwanted noise,and to provide, through an amplifier, suitable level adjusting as isappropriate for the circuitry being fed thereby. For instance, thesignal conditioners 56 scale the signals to the proper level so thateach of them can be fed through a common A/D converter 12 (FIG. 1). Thesignal conditioners 56, 57 can be suitable ones of a wide variety knownin the art, and form no part of the present invention.

Referring now to FIG. 3, the tooth timer 15 includes a counter 60 whichrepetitively counts clock pulses on a line 61 that may be supplied bysystem clocks 46 in FIG. 1. The counter is parallel-fed to a buffer 62,the output of which comprises the tooth counts. The counter is runningsubstantially all of the time since a very high frequency clock signalcan be utilized on the line 61 (anywhere from tens of KHz to tens ofMHz) whereas at speeds from 300 rpm to 2,000 rpm the frequency of thetooth signals on the line 14 may be on the order of 10 Hz to 10 Hz,depending upon the number of teeth. Thus the few clock signals lostduring the tooth to tooth resetting of the counter are miniscule.

Each time that a tooth signal appears on the line 14, the next clocksignal will set a D-type flip flop 63, the Q output of which is appliedto a D-type flip flop 64. The second clock signal following the toothsignal therefore sets the D-type flip flop 64, and since its Q output isapplied to a D-type flip flop 65 the third clock signal will cause it tobecome set. The very first clock signal, after the appearance of thetooth signal, is decoded by an AND circuit 66 since it responds to Q offlip flop 63 and not Q of flip flop 64 and 65; this provides a loadbuffer signal on a line 67 to cause the buffer 62 to be loaded inparallel from the counter 60. The second clock signal following theappearance of the tooth signal will cause an AND circuit 68 to respondto the Q of flip flops 63 and 64 and the not Q of flip flop 65 so as togenerate a clear counter signal on a line 69 which is applied to theclear input of the counter 60 causing it to be cleared to zero. Thethird clock signal, by setting the flip flop 65, simply eliminates theclear counter signal on the line 69 so that the next leading edge of theclock signal and all subsequent clock signals will be counted in thecounter 60. Whenever the tooth signal disappears, (which is totallyimmaterial) the next three clock signals in a row will cause resettingof the flip flops 63-65, in turn, since each of their D inputs will godown. The counter and the buffer are independent of the resetting of theflip flops 63-65 since both AND circuits 66, 68 operate only during aprogression with flip flop 63 on and flip flop 65 off, which does notoccur during the resetting of the flip flops.

Thus the tooth timer 15 provides tooth counts on the line 16 which arestable, throughout substantially each intertooth interval. Theprocessing apparatus of FIG. 1 may therefore sample the tooth counts atrandom. The tooth timer 15 thereby provides very accurate, sub-cyclicspeed measurement, on a tooth to tooth basis, which provides speedindications many times within each individual cylinder stroke portion ofeach engine cycle.

In the detailed description of exemplary processing hereinafter, theterm "ringgear" is sometimes used in place of "flywheel"; they mean thesame thing; the abbreviation "RGT" means "ringgear teeth", a storedfactor indicating the number of teeth on the flywheel of the engineunder test. This may be determined and entered from enginespecifications, or as set forth in a commonly owned copendingapplication of Stick et al, Ser. No. 684,037, entitled "Determination ofNumber of Teeth on an Internal Combustion Engine Flywheel". Otherabbreviations include: "RSLT" = result register; "MEM" = memory; "Ctr" =counter; "Factor" means a memory location or a register where the factoris available; "CMPLT" means A/D conversion is completed; "spd" meansspeed; and other abbreviations are apparent in the drawing.Parentheticals after "MEM", such as "(Freq)", indicate addresses, chosenat will by the programmer, or partially determined by counter two, if soindicated.

The exemplary system herein is designed for four-stroke, six-cylinderengines. If desired, the programming may be altered to compare counts(particularly counter two) with loaded indications of engine variables,such as cylinders, in a well known fashion.

The present invention accurately measures speed at two points in time,as an engine is accelerating with its own inertia, drag, and engineaccessory load for loading, at a first point and a second point whichare spread substantially across the acceleration pattern of the enginefrom low idle to high idle. The invention utilizes instantaneous speed,measured on a sub-cyclic basis, to provide a very accurate correlationbetween speeds measured at the low and the high ends of the accelerationpattern and the time interval between the speed measurements. Theinvention may be practiced in either of two ways, depending on anyparticular implementation thereof. A first manner of practicing thepresent invention is to sense a predetermined starting speed at the lowend of the acceleration pattern of the engine, and starting an intervaltimer having a fixed time out interval. When the interval timer timesout, a second speed measurement is immediately made. The second speedmeasurement is the only unknown, since the time between them and thefirst speed measurement are predetermined. The second method ofpracticing the present invention is to sense a first speed at the lowend of the acceleration pattern of the engine, start an interval timer,sense a second predetermined speed at the high end of the accelerationpattern, and stop the interval timer. In this case the time measured bythe interval timer is the only unknown since the starting and stoppingspeeds are predetermined.

The speed measurements herein are made by the tooth timer, which sensesthe passage of teeth and records a count of the number of clock signalsfed to a counter on a tooth-to-tooth basis. The fraction of a revolutiontraversed as each tooth passes the sensor is simply the ratio of onedivided by the total number of teeth. The time for that fraction of arevolution to occur is simply the counts of the interval timer dividedby the frequency of clock signals fed to the interval timer. Sincefrequency of the clock feeding the counter is expressed in Hz, and speedis normally expressed in revolutions per minute, a factor of 60 must beemployed in a well known fashion. To actually determine the speed fromthe counts provided by the tooth counter the relationship is the ratioof one tooth to the total number of teeth, which is divided by the ratioof the counts to the frequency (the frequency in turn having to be firstdivided by 60 to yield a result in rpm's). Rewritten this results in thefrequency of the clock times 60, all of which is divided by the totalnumber of flywheel teeth times the counts in the timer. This may bepredetermined as a speed factor, so that any time a speed reading isrequired, it can be taken simply by dividing the speed factor by thenumber of counts in the timer, according to the following instructions:

1. Load MEM (Freq) to A REG

2. Load MEM (RGT) to B REG

3. Divide

4. Load RSLT to A REG

5. Load 60 Factor to B REG

6. Multiply

7. Load RSLT to MEM (Spd Factor)

On the other hand, when comparing the actual speed of the engine asdetermined by the tooth timer with predetermined speeds (such as thestarting speed for horsepower measurement) one can reverse the positionof speed and counts in the relationships described hereinbefore anddetermine in advance the number of counts which the tooth timer willhave when the engine has a predetermined speed. This is done generallyby multiplying the frequency of the clock times 60, all of which isdivided by the product of the total number of teeth on the flywheel andthe desired starting speed in rpm. This can be accomplished in theexemplary diagnostic system of FIG. 1 with the following instructions.

8. Load MEM (Freq) to A REG

9. Load MEM (RGT) to B REG

10. Divide

11. Load RSLT to A REG

12. Load MEM (Start Spd) to B REG

13. Divide

14. Load RSLT to A REG

15. Load 60 Factor to B REG

16. Multiply

17. Load RSLT to B REG

Then the system can simply monitor the tooth timer counts, continuouslysubtracting the tooth timer counts from the predetermined counts. Sincecounts become smaller and smaller as the speed increases, when the speedof the engine exceeds the predetermined speed, then the predeterminedcounts will exceed the tooth timer counts and this can be determined bydoing a reverse subtract and looking for a negative result as set forthin the following instructions:

18. Load Tooth timer to A REG

19. Subtract; Skip one if -

20. Branch to 18

In the present example, it is assumed that an interval timer of aconstant time interval is being utilized, so that when the timer timesout, the second speed reading must be made. This speed reading is madeby comparison with the precomputed speed factor (instructions 1-7) asdescribed hereinbefore. An exemplary process may be in accordance withthe following instructions:

21. Start Interval timer

22. Skip 1 if time out

23. Branch to 22

24. Load Tooth timer to B REG

25. Load MEM (Spd Factor) to A REG

26. Divide

27. Load RSLT to A REG

28. Load MEM (Start Spd) to B REG

29. Subtract

30. Load RSLT to MEM (wherever desired)

The particular manner in which the tooth speeds and time are utilizedforms no part of the present invention. It is known that torque is theproduct of inertia and acceleration, and that torque at a given speed isrelated to horsepower. There are many methods in the prior art known forutilizing these factors, most of which employ some sort of empericallydetermined constant to provide a more accurate relationship between thegross acceleration sensed (the difference in the two speeds over thetime interval measured) to a meaningful relationship with respect tohorsepower.

The second method in which the present invention may be practiced doesnot utilize a fixed time interval, but utilizes fixed starting andstopping speeds, and senses the time interval, which may be inaccordance with the following instructions:

31. Load MEM (Freq) to A REG

32. Load MEM (RGT) to B REG

33. Divide

34. Load RSLT to A REG

35. Load MEM (End Spd) to B REG

36. Divide

37. Load RSLT to A REG

38. Load 60 Factor to B REG

39. Multiply

40. Load RSLT to B REG

41. Load Tooth timer to A REG

42. Subtract; Skip one if -

43. Branch to 32

44. Stop Interval timer

45. Load Interval timer to MEM (wherever desired)

Thus, the invention senses speed so quickly, on a sub-cyclic basis, thatit can provide an accurate relationship between two speeds and aninterval between the two speeds, during an acceleration pattern of anengine, so as to provide meaningful information which may be used in anydesired fashion, and as had been used in the prior art to formulate someindication of horsepower. Because the invention can measure speedinstantaneously, there is no need for any fudge factors to accommodatecyclic speed measurements, which are frequently off by tens of percents.

Although the invention has been shown and described with respect topreferred embodiments thereof, it should be understood by those skilledin the art that the foregoing and various other changes, omissions andadditions be made therein and thereto without departing from the spiritand the scope of the invention.

Having thus described typical embodiments of my invention, that which Iclaim as new and desire to secure by Letters Patent is:
 1. Apparatus forproviding indications of speed of an internal combustion engine at twopoints in time, spaced across a significant portion of an accelerationprofile of the engine while accelerating, together with an accuratemeasure of the elapsed time between the two speed measurements,comprising:means for registering indications of a starting thresholdspeed and an ending threshold speed and providing a start speed datamanifestation and an end speed data manifestation in response thereto;speed sensing means, adapted to be disposed for response to a mechanicalmovement of a portion of the engine through successive angles which area small fraction of a full revolution of the engine, for successivelyproviding measured data manifestations of the time elapsed duringangular revolution of the engine through said known angle; an intervaltimer operative in response to command input signals applied thereto tocommence timing of an interval and to cease timing of an interval and toprovide an elapsed time manifestation indicative of the interval of timemeasured thereby; and processing means responsive to said speed sensingmeans and to said registering means for comparing said measured datamanifestation against said start manifestation and said end datamanifestation and for providing a start command input signal to saidinterval timer in response to said measured data manifestationsindicating a speed as high as the speed represented by said start datamanifestation, and responsive to said measured data manifestationindicating that the engine has achieved a speed equal to said end speedmanifestation to provide a stop command input signal to said intervaltimer.
 2. In the method of providing indications of speed of an intervalcombustion engine at two points in time spaced across a significantportion of an acceleration profile of the engine while accelerating,together with an accurate measure of the elapsed time between the twomeasurements, the steps of:providing indications of a starting thresholdspeed and an ending threshold speed; measuring the instantaneous speedof the engine by monitoring mechanical rotation of a portion of theengine through successive angles which are a small fraction of a fullrevolution of the engine; and repeating the speed measuring step andcomparing the speed to said starting threshold speed until the speedexceeds the starting threshold and in response thereto starting aninterval timer operative to provide an elapsed time manifestationindicative of the interval of time measured thereby, repeating the speedmeasuring step and comparing the speed to said ending threshold speeduntil the speed exceeds the ending threshold and in response theretostopping the interval timer.
 3. Apparatus for providing indications ofspeed of an internal combustion engine at two points in time, spacedacross a significant portion of an acceleration profile of the enginewhile accelerating, together with an accurate measure of the elapsedtime between the two speed measurements, comprising:means forregistering indications of a starting threshold speed and providing astart speed data manifestation in response thereto; speed sensing means,adapted to be disposed for response to a mechanical movement of aportion of the engine through successive angles which are a smallfraction of a full revolution of the engine, for successively providingmeasured data manifestations of the time elapsed during angularrevolution of the engine through said known angle; an interval timeroperative in response to command input signals applied thereto tocommence timing of a fixed interval and to provide a time-out signalafter the interval of time measured thereby; and processing meansresponsive to said speed sensing means and to said registering means forcomparing said measured data manifestation against said startmanifestation and, in response to said measured data manifestationindicating a speed as high as the speed represented by said start datamanifestation, for providing a start input command signal to saidinterval timer and responsive to said time-out signal to register ameasured data manifestation indicating the engine speed at the time-outof said interval timer.
 4. In the method of providing indications ofspeed of an interval combustion engine at two points in time spacedacross a significant portion of an acceleration profile of the enginewhile accelerating, together with an accurate measure of the elapsedtime between the two speed measurements, the steps of:providing anindication of a starting threshold speed; measuring the instantaneousspeed of the engine by monitoring mechanical rotation of a portion ofthe engine through successive angles which are a small fraction of afull revolution of the engine; repeating the speed measuring step andcomparing the speed to said starting threshold speed until the speedexceeds the threshold speed and in response thereto starting an intervaltimer operative to time a fixed interval and to provide a time-outsignal after said fixed interval of time has elapsed; and sensing thetime-out signal from said interval timer and in response theretorepeating said speed measuring step and recording speed measuredthereby.